This project concerns the development of children's teleological tendency to view objects as "designed for a function." For adults, teleological assumptions provide a critical basis for explanation and inference about artifacts, such as chairs, and biological structures, such as eyes, (Dennett, 1987). Previous studies suggest however, that, in contrast to adults, young children also construe non-living natural objects, such as rocks, as designed for a purpose. The major goal of the current proposal is to understand why children over-attribute function to non-biological natural kinds by studying developmental progressions in 3- to 6-year-olds conception of the relationship between the design, function and identity of artifacts. There are several reasons for focusing on artifacts to explore this question. First, for adults, artifacts provide the clearest instance of objects that exist for a function because their occurrence is entirely explained by a designer's intention that they fulfill some goal. Second, one hypothesis as to why children explain the properties of entities such a rocks in teleological terms is that in the absence of alternative accounts, they treat them as intentionally-designed quasi- artifacts (Kelemen, 1998; also Piaget, 1929). The proposed studies aim to replicate, extend, and clarify prior work on children's and adult's teleological thought using a variety of experimental methods and an expanded age range. One set of studies uses behaviorally-active methods to examine whether children view their own intentions as fixing the function and identity of an artifact that they have just designed. A second set of studies manipulates information about the origin and current use of a novel artifact in order to study its influence on children's judgments of the object's identity and function. A final set of studies explores the degree to which young children fall prone to the classic psychological phenomenon of "functional fixedness." Using these methods to understand the status of children's teleological beliefs about artifacts will provide needed insight into the formation and development of children's intuitive and scientific theories about both the artificial and natural world.